An exhaust manifold is a pipe that conducts the exhaust gases from the combustion chambers to the exhaust pipe. The size and design of the exhaust manifold is closely related with the power of engines because the manifold is located in the first portion to receive exhaust gases from the head.
Conventional oxidation resistant cast irons such as FCD50M, FCD45F, FCD-H, and FCD-50HS have compositions in Table 1. These cast irons contain Si and/or Mo added to the conventional spherical cast iron to improve physical properties and oxidation resistance at high temperature.
TABLE 1Prior Art Cast Iron FormulationsProductsCSiMnPSCrMgMoNiFeFCD50M3.0-2.0-0.2-0.6BelowBelowBelowAbove——Balance4.03.01.00.020.30.025FCD-J3.0-2.0-0.2-0.6Below——Above—BelowBalance4.03.00.10.0151.0FCD-M3.0-3.8-BelowBelowBelow—0.04-0.5-—Balance4.04.00.6 0.040.020.0650.7FCD-H3.2-3.2-Below———Above——Balance3.93.80.30.02 FCD50HS3.3-3.4-BelowBelowBelow—Above0.4-BelowBalance3.83.80.60.10.0150.0250.51.0
There are three requirements of the metal—high temperature strength, high temperature oxidation resistance both (when exposed to the atmosphere and also when exposed to exhaust gases), and compatibility with catalysts. If an exhaust system using heat resistant cast iron is held at a temperature of 630° C. to 760° C. which may typically be encountered in use, tensile strength of the prior art oxidation resistant cast irons is generally at least about 75 Mpa. However, the strength of cast iron metals declines with temperature.
The various grades of austenitic cast iron display a wide variety of properties, which is why they are being employed in numerous technical applications. The DIN 1694 standard recognizes eight lamellar-graphite and fourteen spherolitic-graphite variants. Their outstanding properties include high-temperature stability, oxidation resistance, unusual heat-expansion coefficients (from high to low), favorable running properties, corrosion resistance, low-temperature toughness, and erosion resistance. An austentic cast iron according to DIN 1694 may have up to 3% carbon, 1.5-3% Si, 0.5-1.5% Mn, 18-22% Ni, and 1-2.5% Cr.
Recent innovations in design of exhaust system of automobiles requires the iron to have high performance (high tensile strength) at a temperature of 730° C. to 900° C. It is also advantageous to produce the exhaust system with a cast iron having excellent oxidation resistance at elevated temperatures, and also with high catalyst compatibility to be responsive to restrictive regulations on exhaust gases that result from increase in the power of automobiles. Conventional cast iron cannot properly meet these criteria. Therefore, the demand to obtain materials having superiority in these many characteristics has been highly increased.